With the retirement of Rep. Howard “Buck” McKeon, the battle to represent his district in north Los Angeles County becomes the main event among Southern California’s 2014 congressional elections.

McKeon made it official today in Washington: The 75-year-old Republican won’t seek re-election after 21 years in the House. He served the past three years as chairman of the Armed Services Committee, earning praise from Speaker John Boehner as “a tireless advocate for our military and Department of Defense civilian personnel, as well as their families.”

The news was expected. Already planning to run in the June 3 primary for the 25th District seat were state Sen. Steve Knight and former state Sen. Tony Strickland, both Republicans, and Lee Rogers, the Democrat who lost to McKeon in 2012.

Republicans had a 5.3 percentage-point edge over Democrats in 2012 in the district that stretches from Simi Valley to the Antelope Valley across the top of the San Fernando Valley. Mitt Romney beat President Obama by 2 percentage points there.

It’s one of those races where California’s “top-two” primary system could send two candidates from the same party into the general election — or the two leading Republicans could split their party’s voters and let a Democrat sneak in.

There will be other congressional races to watch in Southern California this year. Two that leap to mind: Rep. Gary Miller, R-Rancho Cucamonga, trying to hold off Democratic former Rep. Joe Baca and Redlands Mayor Pete Aguilar in the majority-Democratic 31st District; and Rep. Henry Waxman, D-Manhattan Beach, facing a celebrity challenger in spiritual author Marianne Williamson in the 33rd District.

But so far, the race for McKeon’s job is the biggest, and one where voters should really pay attention.

As we see from McKeon — and other House veterans announcing their retirements lately — people who are elected to Congress for the first time tend to hold power for a long time.